1. Field of the Invention
The present invention relates to a brake pressure control system for a vehicle, and more particularly to the system having a pressure generating device for generating a first pressure and a second pressure having different pressure characteristics.
2. Description of the Related Arts
A brake pressure control system as disclosed in a Japanese Patent Laid-open Publication No. 3-227766 is adapted to increase a brake force applied to a wheel of a vehicle according to a brake operating force applied by a driver, when an emergency brake operation by the driver is detected. According to the brake pressure control system disclosed in the publication, when the emergency brake operation is detected, an electromagnetic valve connected to a variable chamber of a vacuum booster is placed in its open position for introducing a large volume of atmospheric air into the variable chamber thereby to increase the brake force. As a result, a stopping distance is shortened in case of the emergency brake operation, comparing with that in case of an ordinary brake operation. In the brake pressure control system as described above, however, it is necessary to provide the electromagnetic valve connected to the variable chamber, so that a large modification in structure to the vacuum booster is required, which causes increase in cost.